The present invention relates to a barrier-forming film and a manufacturing method thereof. More particularly, the invention relates to a barrier-forming film which has a higher barrier-formability preventing permeation of oxygen gas, steam or the like and is useful for manufacturing various packaging containers and a manufacturing method thereof.
For the purpose of filling-packaging eatables and drinkables, chemicals and the like, packaging containers of various forms have conventionally been developed and proposed. In these packaging containers, barrier-forming materials of various forms including plastic films are usually used as materials composing packaging containers with a view to preventing deterioration of contents, and in addition, improving shelf life and storage life.
More recently, the general attention is attracted to a transparent barrier-forming film having a vapor-deposited inorganic oxide film such as silicon oxide or aluminum oxide provided on a side of a substrate film comprising a biaxially oriented polyethyleneterephthalate film or a biaxially oriented nylon film as one of barrier-forming materials, and packaging containers of various forms using such a material have been developed and proposed.
As compared with conventional barrier-forming materials comprising a plastic film such as a polyvinylidene chloride-based resin or a polyvinylalcohol-based resin or a barrier-forming material comprising a metal layer having a resin film having a vapor-deposited aluminum film, the recently developed and proposed one has a function of barrier-formability equal to or even superior to that in the conventional art in terms of barrier-formability of preventing permeation of oxygen gas and steam, particularly excellent in disposability of waste container packages. For example, the new barrier-forming material is excellent in advantage for coping with environments in that it does not cause ecocide even when applying disposal such as incineration, so that an increasing use and demand are expected hereafter as a barrier-forming material for making packaging containers.
However, in a transparent barrier-forming film comprising, as a barrier-forming material, having a vapor-deposited silicon oxide, aluminum oxide, or other inorganic oxide film formed on one side of a substrate film made of the above-mentioned biaxially oriented polyethyleneterephthalate or biaxially oriented nylon, it is very difficult to prepare vapor-depositing conditions including, for example, the kind of substrate film, the vapor-depositing rate, the chemical composition of vapor-depositing pressure, the vapor-depositing gas flow rate, the degree of vacuum, the vapor deposition output, the temperature upon vapor deposition and the like. Film forming of a vapor-deposited film of an inorganic oxide such as silicon oxide or aluminum oxide alone cannot ensure manufacture of a barrier-forming material excellent in prevention of permeation of oxygen gas or steam.
For example, in order to manufacture a barrier-forming film having constant and stable function of preventing permeation of oxygen gas or steam, which is the most important function as a barrier-forming material, therefore, it is very difficult to work out vapor-depositing conditions: problems are often caused in that there occur fluctuations between product lots or rejects are produced in a large quantity.
In the transparent barrier-forming film having a vapor-deposited film of an inorganic oxide such as silicon oxide or aluminum oxide formed on one side of a substrate film comprising a biaxially oriented polyethyleneterephthalate film or a biaxially oriented nylon film, in terms of barrier-formability, the steam permeability is substantially 10.0 g/m2.day, and the oxygen permeability is about 10.0 cc/m2.day.atm. It is therefore practically difficult to manufacture a transparent barrier-forming film having a steam permeability of up to 5.0 g/m2.day and an oxygen permeability of up to 5.0 cc/m2.day.atm.
Furthermore, in the case of a transparent barrier-forming film using a transparent biaxially oriented polyethyleneterephthalate film or a biaxially oriented nylon film and having a vapor-deposited film of an inorganic oxide such as silicon oxide, the product is a yellowish or yellow-brownish barrier-forming film, although the reason is not as yet known. This results in a problem in that it impairs transparency or decorativeness by printed patterns, thus preventing a satisfactory packaging material or a packaging container from being manufactured.
The present invention has therefore an object to provide a barrier-forming film which has a high barrier-formability for preventing permeation of oxygen gas or steam, and is useful for manufacturing various packaging container.
After carrying out repeated study efforts about the above-mentioned transparent barrier-forming film, the present inventor took note of the fact that, in a transparent barrier-forming film having a vapor-deposited film of an inorganic oxide such as silicon oxide or aluminum oxide formed on one side of a substrate film comprising the above-mentioned biaxially oriented polyethyleneterephthalate film or a biaxially oriented nylon film, the substrate film thermally shrank and the yellowish or yellow-brownish color tone of the vapor-deposited film of the inorganic oxide changed by applying an annealing treatment comprising a heat treatment. First, they manufactured a transparent barrier-forming film by forming a vapor-deposited film of an inorganic oxide such as silicon oxide or aluminum oxide on one side of the substrate film of the above-mentioned biaxially oriented polyethyleneterephthalate film or biaxially oriented nylon film. Then, an annealing treatment comprising a heating treatment of setting a heat treatment temperature of at least room temperature and holding the object in an oven for 24 hours was applied to the transparent barrier-forming film. The substrate film composing the transparent barrier-forming film shrank and the vapor-deposited inorganic oxide film became denser. Furthermore, the yellowish or yellow-brownish tone upon forming the vapor-deposited inorganic oxide film changed, bringing about an improvement of the degree of yellowing from the yellowish or yellow-brownish tone upon film forming, thus increasing transparency. The amount of change in X-value of the inorganic oxide such as silicon oxide or aluminum oxide as expressed by a formula MOx for composing the vapor-deposited inorganic oxide (where, M represents a metal element; the range of values of X varies between metal elements) increases slightly, In addition, there was a change in surface roughness of the vapor-deposited inorganic oxide film. The barrier-formability for preventing permeation of oxygen gas or steam was remarkably improved as a barrier-forming material forming a packaging container. The present inventor thus obtained findings of the possibility to manufacture a barrier-forming film useful for manufacturing various packaging containers, and completed the present invention.
More specifically, the present invention relates to a barrier-forming film comprising a substrate film having a vapor-deposited inorganic oxide film, subjected to an annealing treatment, wherein the steam permeability is within a range of from 2.0 to 0.000001 g/m2.day, and the oxygen permeability is within a range of from 2.0 to 0.000001 cc/m2.day.atm, and a manufacturing method thereof.